Clinical Challenge: January, 2015

Resolution

DDx
Community-acquired methicillin-resistant Staphylococcus aureus (MRSA) infection
Caterpillar envenomation
Contact dermatitis
Ecthyma
Solar purpura
 
Learnings
Common spider bites usually present with erythema and edema. A necrotic or dusky center within a red, inflammatory plaque is characteristic.
 
In brown recluse spider bites, vesicles and bullae can present early. Between 12 and 24 hours after envenomation, a large plaque consisting of erythema, ischemia, and necrosis (“red, white, and blue” sign) develops. Later, these lesions can progress into painful, full-thickness necrotic plaques.
 
Patients with black widow bites have local sweating, piloerection, redness, and mild edema. The systemic symptoms of muscle pain, cramps, abdominal pain, salivation, lacrimation, sweating, and tremors are more prominent than the skin findings.
 
If the victim brings in the spider, seek out a trained arachnologist or entomologist for accurate identification.
 
Diagnostic Pearls
Look closely for 2 small puncta, the fang marks of the spider. Most suspected spider bites seen in the United States turn out to be the result of other causes, most commonly cellulitis or furunculosis caused by MRSA. Unless the spider has specifically been identified as the etiology of the symptoms, be cautious about narrowing your differential diagnosis and consider culturing for MRSA.